Recent developments in optical fibers and materials with low transmission losses have enhanced the attractiveness of integrated optical circuits. Although these circuits can be realized as discrete components, the advantage of integrating devices in solid-state systems is widely appreciated. Such solid-state systems will require a solid-state, electrically excited, laser light source to producea high intensity, coherent light beam.
Solid-state laser devices having either planar or cleaved end mirrors or other external mirrors are not suitable for integrated structures. Generally, the mirrors are displaced from each other by a very large multiple of half wavelengths, for example, thousands of half wavelengths. Thus, the mirrors can reinforce light of many different wavelengths thereby making it very difficult to provide good frequency selectivity and stability. Further, lasers having cleaved or external end mirrors may require higher threshold current densitities which act to decrease operating life.
Recently, interest has been focused upon distributed feedback lasers. These structures do not utilize the conventional cavity end mirrors, but instead provide feed-back by means of Bragg Scattering from periodic perturbations of the refractive index and/or gain of the laser medium itself. Distributed feedback lasers are compact and provide a high degree of frequency selectivity. However, as yet no one has successfully applied this distributed feedback concept to obtain oscillations in electrically pumped solid-state lasers. If such a laser was capable of 300.degree. Kelvin (room temperature) operation, it could become the primary light source for proposed integrated optical circuits.
State-of-the-art distributed feedback solid-state and solid-dye lasers utilize optical pumping and thus require an independent light source. Such an independent pumping source, which itself can be a laser device, and its associated focusing optics, are hard to align properly for the desired impingement, and, obviously, a separate laser pumping source is not compatible with an integrated optical circuit.
It is an object of the present invention to provide a method of making an improved electrically pumped solid-state laser device.
It is a further object of the present invention to provide an improved method of making an electrically pumped single heterojunction distributed feedback laser device.
It is still further object of the present invention to provide an improved method of making an electrically pumped, double heterojunction distributed feedback laser device.